1. Field of the Invention
The present invention relates generally to latches, and more particularly to an improved latch for a cassette such as an X-ray film cassette or the like.
2. Description of the Prior Art
The prior art is replete with latches for X-ray film cassettes of which U.S. Pat. Nos. 3,153,145 and 3,323,676 are exemplary.
U.S. Pat. No. 3,153,145 discloses a latch for a cassette having a latch plate on one panel and a catch spring on the other panel. When the plate and spring are moved into engagement, they releasably latch the panels together. The latch further has a pivotal latch operating lever mounted on one panel. Pivotal movement of the latch operating lever causes the free end of the lever to engage the catch spring and disengage it from the latch plate for releasing the panels. The pivot means for the latch operating lever comprises a pivot shaft on the panel, and depending side flanges on the lever through which the shaft is journaled for relative rotational movement.
U.S. Pat. No. 3,323,676 discloses a cassette latch having a latch operating lever pivotally mounted on a shaft supported by one panel. The latch operating lever has two parts welded together to form an opening therebetween for receiving the shaft. The lever further has a handle at one end, and a rigid hook at the other end biased into engagement with a rigid catch member on the other panel for releasably latching the panels together.
A commercially available X-ray film cassette known in the art comprises a latch operating lever mounted on one of the panels for pivotal movement about a rigid shaft secured to the panel. The latch operating lever has a pair of lugs movable therewith into engagement with an L-shaped catch plate, also pivotally mounted to the shaft. The lugs retract the catch plate from a latch plate on the other panel for releasing the two panels. A pair of helical springs are mounted on the shaft, one interposed between the latch operating lever and panel and the other interposed between the catch plate and panel for normally urging the latch operating lever and catch plate into normal and latched positions respectively.
A problem with the latches disclosed in the prior art is that the pivot means comprising shafts and shaft supports such as flanges, are subjected, due to the geometry of the latches, to considerable forces and stresses with repeated use of the latches. Such forces in time will cause the shaft and flanges of the latches to wear and eventually to fail. When this occurs, the cassette has to be rebuilt, if possible, or discarded, both options of which are costly.
Other problems with the prior art latches are their unreliability, complexity, and high cost of manufacture, due primarily to the number of high precision latch parts involved, and the time consuming manufacturing operations required to assemble and produce the latches.